In general electrophotography, an electrostatic latent image is formed through various means on a photoreceptor comprising a photoconductive substance, such as selenium, and a toner is deposited on the latent image by magnetic brush development, or like technique, to make visible the latent image.
In the aforesaid development processing, particles called "carriers" are used to impose an appropriate quantity of positive or negative charge on toner particles. Carriers are generally divided into coated carriers and non-coated carriers. Because coated carriers have a superior working life in developers, and the like, various kinds have been developed and put into practical use.
Among various performance characteristics required for the carrier, particularly important are proper charging properties, impact resistance, abrasion resistance, satisfactory adhesion between the core and the coating material, uniformity of charge distribution, and the like. Taking these characteristic requirements into consideration, the conventionally known coated carriers still leave room for improvement, and none of them is quite satisfactory. For example, although fluorinated vinyl polymers, proposed as a coating material in U.S. Pat. Nos. 3,922,382 and 3,798,167, satisfy resistance to surface contamination, they have poor adhesion to a magnetic core. Acrylic polymers as described in JP-A-47-13954, though satisfactory in mechanical strength and adhesion to a core, are insufficiently resistive to surface contamination and have poor charging properties. Thus, the state-of-the-art coated carriers employ coating materials having both merits and demerits.